FIG. 1 shows an optical transmission element 10 containing four optical waveguides 1a, 1b, 1c and 1d in its interior. The optical waveguides are embedded into a protective layer 2. The protective layer 2 contains a UV-curing acrylate, for example. The protective layer 2 is surrounded by an outer sheath 3.
In order to protect optical transmission elements against tensile and compressive loading and also in order to afford protection against contamination, optical transmission elements are guided in empty conduits. The optical transmission elements are blown into the empty conduits by compressed air. The empty conduits are formed as plastic conduits having an outer diameter of approximately 5 millimeters and an inner diameter of approximately 3.5 millimeters.
The length with which an optical transmission element can be blown into an empty conduit is a significant quality feature. Typical blow-in lengths are between 500 meters and 1000 meters, which have to be achieved under different climatic conditions. In order to reduce a frictional resistance when an optical transmission element is blown into an empty conduit, the empty conduit generally has an inner coating affording slidability.
The document U.S. Pat. No. 5,557,703 describes an embodiment of an optical transmission element which is used for blowing into an empty conduit. In order to improve the blow-in behavior and in particular in order to reduce a friction between the optical transmission element and the inner wall of the empty conduit, spherical elements are disposed on a surface of the outer sheath of the optical transmission element. In this case, the coefficient of friction of the spherical elements is preferably lower than the coefficient of friction of the material used for the inner wall of the empty conduit.
FIG. 2 shows the outer sheath 3 of an optical transmission element with spherical elements applied on said sheath.
Despite such measures, a friction process between the outer sheath of the optical transmission element and the inner wall of the empty conduit cannot be avoided when an optical transmission element is blown into an empty conduit. Possible blowing-in lengths within the range of between 500 meters and 1000 meters as specified above are achieved, however, only when electrostatic charging of the optical elements is avoided by suitable measures during a blow-in operation. When the optical transmission elements are blown in, charging of the optical transmission elements generally occurs as a result of the friction of the optical transmission elements at the inner coating of the empty conduit. The charges on the surface of the optical transmission elements lead to a high degree of adhesion on account of the electrostatic attraction between the optical transmission elements and the inner wall of the empty conduit.